1. Field of the Invention
The present invention relates to swage mounts for hard disk drives and methods of manufacturing swage mounts.
2. Description of Related Art
In hard disk drives, data are stored on surfaces of a plurality of rotatable disks mounted on a housing of the drive. An actuator positions transducer heads in alignment with concentric data tracks defined on the disks. The transducer heads write data to and read data from the disk surfaces. Each transducer head is attached to one end of a head suspension that is connected to an actuator arm that extends from the actuator body.
FIG. 1 is a top view illustration of a head suspension assembly 30 that can be connected to an actuator arm (not shown). The head suspension assembly 30 includes a swage mount 31. The swage mount 31 is made of a base material such as stainless steel. The swage mount 31 has a flange portion 37 that includes a flange body portion 32 connected to a tip portion 33. The tip portion 33 vibrates in-plane and is shaped in the form of the letter ‘T.’ The swage mount 31 optionally includes a through-hole 36. A hub 35 surrounds an aperture of the flange body portion 32 and extrudes out of plane. The head suspension assembly 30 is swaged onto the actuator arm by inserting and swaging the hub 35 into a hole in the actuator arm.
Primary actuation is performed, for example, using a voice coil motor integrated into the actuator arm. In addition, at least one of a secondary actuation near the swage mount 31 or a direct movement of the head near the flexure 25 can be performed. The flexure 25 locates the head, which is bonded underneath the flexure 25. The flexure 25 locates the head rigidly in the x-z plane while allowing the head to rotate. The head can fly very closely to the disk surface without contacting it in order to read and/or write small magnetic bits. Rotation of the head maintains proper fly height and attitude with respect to the disk.
Piezoelectric transducers (PZTs) 17 are provided as secondary actuators that mechanically position the head in a planar direction in response to applied electrical charge. The PZTs 17 include surfaces covered with conductive material such as gold. The gold-covered top surface can be the ground side of the PZT 17. The ground path passes through the swage mount 31, the swaged hub, the actuator arm and the actuator arm connection. Conductive contacts 19 connect the PZT 17 to a ground path. The gold-covered bottom surface can be connected to an electronic circuit (e.g., an electronic circuit for the flexure 25). Alternatively, the bottom surface can be the ground side, and the top surface can be the circuit connection. The bottom and/or top surfaces of the PZTs 17 can be connected to other electrical components in the drive. The conductive contacts 19 can be silver filled epoxies for providing a conductive link between the swage mount 31 and the PZTs 17. Alternatively, the contacts 19 are soldered conductive contacts.
The conductive contacts 19 can be positioned on different locations based on design concerns. FIG. 1 shows the conductive contacts 19 positioned between the PZTs 17 and the cross-bar part of the ‘T’-shaped tip portion 33. FIG. 2 shows that the conductive contacts 19 are positioned on an opposite side of the PZTs 17, thereby connecting the PZTs 17 to the flange body portion 32.
FIG. 3 shows the swage mount 31 in isolation. The PZTs 17 actuate the head to move or vibrate in the x-z plane. The PZTs 17 bias the ‘T’ shaped tip portion 33 to vibrate substantially in-plane (in the x-z plane). Positive or negative charges are applied to the PZTs 17 resulting in their expansion and/or contraction. As a result, the head is moved for a read/write process on the underlying disk.
The foregoing structure does not provide reliable conductivity for electrically connecting the swage mount 31 to the PZTs 17, or for electrically connecting the swage mount 31 to other components of the drive. Furthermore, the electrical connections and the bond of the electrical contacts significantly degrade after exposure to temperature and humidity changes present in the hard disk drive environment. For example, the electrical connection and the bond between conductive contacts 19 and the stainless steel tip portion 33 is unreliable in part because chromium oxide is formed on the stainless steel surface. Unreliable conductivity results in drive performance failures.
To improve conductivity, prior art swage mounts have been plated with gold in parts on which the conductive contacts 19 are placed. However, this process is unduly expensive. In addition, stainless steel or other base materials with similar characteristics around the gold-plated regions lack sufficient cleanliness. Exposed hard particles or metal oxides of the base materials shed and cause drive failures. Gold particles and base metal particles, such as stainless steel, are shed as well in areas of the drive that require to be kept clean for optimal performance. For example, gold particles and stainless steel particles are shed in the head-to-disk interface and the disk surface. The generated base material and gold particles significantly deteriorate hard disk drive performance.
To achieve cleanliness, hard disk drive components other than swage mounts are plated with nickel. Nickel-plated surfaces shed fewer particles than un-plated stainless steel or aluminum surfaces. Nickel surfaces are also more easily cleaned of foreign contaminants before drive assembly. The few shed nickel particles are less harmful to drive performance than metal oxide particles or other metal particles such as stainless steel, gold or aluminum particles. High phosphorous content electroless nickel plating is most commonly used. However, nickel-plated surfaces are not sufficiently conductive and cannot support a reliable electrical connection. Nickel oxides and other nickel surface properties of a nickel-plated surface negatively impact electrical reliability of conductive contacts 19 positioned thereon after environmental exposure.
Furthermore, commonly used nickel plating such as electroless nickel is not sufficiently ductile and therefore fractures during the swaging process. One or more swage balls are passed through the inside diameter of the hub 35 in the swaging process. The balls are larger than hub 35 such that the hub 35 is permanently deformed. The hub 35 is press-fit or swaged into the swage hole of the actuator arm. Plated material that is not ductile enough or not adhered well to the swage mount fractures when swaging force and torque are applied. The fractured material sheds a significant amount of particles, thereby causing drive failure.
There is a need in the art for a swage mount and method of manufacturing the swage mount that significantly reduces generation of particles that impact hard disk drive performance. There is also a need in the art for a swage mount and method of manufacturing the swage mount that can support a reliable electrical connection even after environmental exposure.